The present invention generally relates to radio communication systems, and more particularly, to a radio communication system, a radio controller and a mobile station in which at least one base station transmits a plurality of the same information to the mobile station via a plurality of radio links.
In this technical field, a radio controller and a base station have UL/DL Node Synchronization functions.
The UL/DL Node Synchronization is performed in order to measure more accurately the transmission delay between the base station and the radio controller when starting and resuming the base station. An explanation of this UL/DL Node Synchronization is given below with reference to FIG. 1.
First, the radio controller transmits a DL Node Synchronization signal to the base station. The DL Node Synchronization signal includes transmission timing information T1 that means the radio controller transmitting time. The Synchronization signal arrives after a transmission delay T2−T1. The T2 means the base station receiving time.
The base station receives the DL Node Synchronization signal and transmits a UL Node Synchronization signal to the radio controller. The UL Node Synchronization signal includes timing information T2 and T3. The T3 means T2+the base station processing delay, and therefore means the base station transmitting time.
The radio controller receives the UL Node Synchronization signal and estimates the timing relation with the base station, based the timing information T1, T2, T3 and T4. The T4 means the radio controller receiving time. The above procedure is repeated at a certain interval, and the timing relation is estimated.
For example, it is defined that Tf is 40960 ms, Tr=Tf−T1, Tb=Tf−T2, and
T_r1=(T1+Tr)modTf;
T_r4=(T4+Tr)modTf;
T_b2=(T2+Tb)modTf; and
T_b3=(T3+Tb)modTf.
Under this situation, a transmission delay T is represented byT={(T—r4−T—r1)−(T—b3−T—b2)}/2
If X1:T2−T1−T, then phase differences (X) between nodes are represented by the following:X=X1+Tf when X1<−Tf/2X=X1 when −Tf/2<=X1<Tf/2X=X1−Tf when X1>=Tf/2
The function of the above explained UL/DL Node Synchronization is not publicly known as of the filing date of this patent application.
The applicant of this patent application has not found any prior art publication relating to the present invention. Therefore, no prior document is disclosed.
However, there is a problem as follows.
In the multicast system, a neighboring cell also transmits the same information. Therefore, mobile stations can receive plural same signals from plural cells via plural radio links, and perform a maximum ratio combining process or a selective combining process. In order to perform such maximum ratio combining process or selective combine process, it is necessary for the mobile station to have the capability of processing plural radio links, including memory, encoding/decoding capability, and so on.
Timing synchronization between cells should not exceed mobile station processing capability. The timing of each cell may vary due to difference in reference clocks.